1. Field of the Invention
The present invention relates to a technology of interfacing between communication networks whose data communication methods are different from each other, more particularly a method for communications of frame relay data to be transmitted and received via the Asynchronous Transfer Mode (ATM) and an apparatus for communications of frame relay data using the frame relay data communication method.
2. Description of the Related Art
A related art technology for transmitting and receiving frame relay data via an ATM switching system is disclosed, for example, Japanese Published Unexamined Application No. 7-202903. This related art technology is characterized as follows; when assembling variable length frame data into fixed length ATM cells, the frame data is converted to intermediate data once, then the intermediate data is divided into fixed-length data to be assembled into ATM cells. The related art technology also refers to a process for assigning service classes to those ATM cells when in assembling of frame data into ATM cells. This is to prevent the ATM switching network from occurrence of congestion. Concretely, the related art discloses two methods for such an assignment of service classes; in order to assign a service class, one of the methods changes the value of the cell loss priority identifier included in the header of each ATM cell corresponding to the communication form specified from an object frame relay terminal and the other of the methods references the discard eligibility indicator (DE) included in the object frame data and copies the value in the cell loss priority identifier.
There is also another invention with respect to a configuration of a frame relay interface circuit used to assemble frame data into ATM cells. The invention is disclosed in Japanese Published Unexamined Application No.6-276215.
The above related art technology includes a method for assigning service classes to ATM cells according to the communication form specified by an object frame relay terminal and the value of the discard eligibility indicator (DE) included in the object frame data. However, the process is nothing but a reference to the communication form or the discard eligibility indicator (DE) included in the object frame data. The processing is just continued fixedly until one communication transaction is ended.
Consequently, when some frame data including various types of data such as video, voice, and data communication data is assembled into ATM cells to be transmitted and received using the related art technology, it has been impossible to assign service classes to those ATM cells according to each data type.
Furthermore, if the order of priority for data types differs between the frame relay network and the ATM network, sometimes the difference causes a problem that some data with a high service class in the frame relay network is regarded to be ordinary data in the ATM network, so that it may be discarded when in a data congestion. For example, alarm information in a frame relay network is very important in the frame relay network, but it is regarded as general data in an ATM network.
The related art technologies described above have also been confronted with a problem that such data as a voice that cannot be delayed so much causes a communication error due to a cell assembly delay.
Furthermore, if the determination process of service class differs among systems so that, for example, priority is given to transmission and receiving of voice data in a system, but priority is given to transmission and receiving of video data in another system, it is also impossible for the related art technologies to change the determination process appropriately to the order of priority for ATM cells.
Under such the circumstances, it is an object of the present invention to provide a method for corresponding the service classes used for various types of data in a frame relay network to the service classes used for ATM cells storing the frame data in an ATM network in order to solve the above related art problems thereby to realize highly reliable communications. It is another object of the present invention to provide a frame relay data communication method for interlocking a frame relay network interface used for connecting a frame relay network to an ATM network with an ATM CLAD (ATM Cell Assembly and Disassembly) apparatus, as well as provide a frame relay data communication apparatus using the frame relay data communication method.
In order to solve the above related art problems, the frame relay data communication method of the present invention comprises steps of; receiving priority order information of data used ATM networks from an ATM network; extracting priority order information from frame data received from a frame relay network so as to decide a service class of the received frame data according to both the priority order information of the data in the ATM network and the priority order information of the received frame data, and then assembling the received frame data into ATM cells according to the decided service class.
The frame relay data communication apparatus of the present invention is provided with a frame receiver unit used to receive frame data from a frame relay network; a cell assembly unit used to assemble the received frame data into ATM cells and transmit the assembled ATM cells to the ATM network; a controller used to control each unit so as to extract the priority order information from the received frame data and receive the priority order information of data used in ATM networks from an ATM network thereby to decide a service class of the received frame data and assemble the received frame data into cells according to the decided service class.